I don't know what you mean by 'code'.  There is no cell format that
restricts a cell to being the recipient of pasted values only.

For a macro you might see if this holds water.  Copy it into the sheet's
module (right click sheet tab and pick View Code):

Private Sub Worksheet_Change(ByVal Target As Range)
   Dim Temp As Variant
   Temp = Target.Formula
   With Application
       .EnableEvents = False
       .Undo
       Target.Formula = Temp
       .EnableEvents = True
   End With
End Sub